linker error when I use template and static variable

Question

I'm trying to make something like this:

class A
{
    static pthread_mutex_t m;
public:
    template<typename T>
        static void TestFunc(T t) {
            pthread_mutex_lock(&m);
    }
    static void Test()
    {
            TestFunc(13);
    }
};

But receive linker error:

/tmp/cc1HN0fI.o: In function void A::TestFunc<int>(int)': TReaderThread.cpp:(.text._ZN1A8TestFuncIiEEvT_[_ZN1A8TestFuncIiEEvT_]+0xc): undefined reference toA::m' collect2: error: ld returned 1 exit status make: *** [all] Error 1

It seems that this error happens only when TestFunc is template function. It is small peace of code, I need that TestFunc was template and my mutex was static variable. Is it possible to solve this issue in template approch? P.S. Realy I need to do - implement tracer as singlton(with syncronization for output descriptor).

You defined m, correct?

Weak to Enuma Elish
– Weak to Enuma Elish

2015-11-23 21:11:57 +00:00
Commented Nov 23, 2015 at 21:11 — Weak to Enuma Elish
– Weak to Enuma Elish, Commented Nov 23, 2015 at 21:11

Marko Popovic · Accepted Answer · 2015-11-24 14:53:42Z

1

Your static pthread_mutex_t m; is declared but is not defined. Add the following line in your *.cpp implementation file:

pthread_mutex_t A::m;

edited Nov 24, 2015 at 14:53

answered Nov 23, 2015 at 21:14

Marko Popovic

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Comments

SEB · Accepted Answer · 2015-11-23 22:59:13Z

0

Template has got nothing to do with the linker error you are getting. What you did inside the class is a declaration. You need to define the static variable outside the class so that memory is allocated and initialized.

answered Nov 23, 2015 at 22:59

SEB

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